Browsing by Subject "observations cosmological interpretation"
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Item The First Galaxies: Assembly Of Disks And Prospects For Direct Detection(2011-04) Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, VolkerThe James Webb Space Telescope (JWST) will enable observations of galaxies at redshifts z greater than or similar to 10 and hence allow us to test our current understanding of structure formation at very early times. Previous work has shown that the very first galaxies inside halos with virial temperatures T-vir less than or similar to 10(4) K and masses M-vir less than or similar to 10(8) M circle dot at z greater than or similar to 10 are probably too faint, by at least one order of magnitude, to be detected even in deep exposures with JWST. The light collected with JWST may therefore be dominated by radiation from galaxies inside 10 times more massive halos. We use cosmological zoomed smoothed particle hydrodynamics simulations to investigate the assembly of such galaxies and assess their observability with JWST. We compare two simulations that are identical except for the inclusion of non-equilibrium H/D chemistry and radiative cooling by molecular hydrogen. In both simulations a large fraction of the halo gas settles in two nested, extended gas disks which surround a compact massive gas core. The presence of molecular hydrogen allows the disk gas to reach low temperatures and to develop marked spiral structure but does not qualitatively change its stability against fragmentation. We post-process the simulated galaxies by combining idealized models for star formation with stellar population synthesis models to estimate the luminosities in nebular recombination lines as well as in the ultraviolet continuum. We demonstrate that JWST will be able to constrain the nature of the stellar populations in galaxies such as simulated here based on the detection of the He1640 recombination line. Extrapolation of our results to halos with masses both lower and higher than those simulated shows that JWST may find up to a thousand star-bursting galaxies in future deep exposures of the z greater than or similar to 10 universe.Item Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results(2013-10) Bennett, C. L.; Larson, D.; Weiland, J. L.; Jarosik, N.; Hinshaw, G.; Odegard, N.; Smith, K. M.; Hill, R. S.; Gold, B.; Halpern, M.; Komatsu, Eiichiro; Nolta, M. R.; Page, L.; Spergel, D. N.; Wollack, E.; Dunkley, J.; Kogut, A.; Limon, M.; Meyer, S. S.; Tucker, G. S.; Wright, E. L.; Komatsu, EiichiroWe present the final nine-year maps and basic results from the Wilkinson Microwave Anisotropy Probe (WMAP) mission. The full nine-year analysis of the time-ordered data provides updated characterizations and calibrations of the experiment. We also provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate cosmic microwave background (CMB) anisotropy from foreground emission, and both types of signals are analyzed in detail. We provide new point source catalogs as well as new diffuse and point source foreground masks. An updated template-removal process is used for cosmological analysis; new foreground fits are performed, and new foreground reduced CMB maps are presented. We now implement an optimal C-1 weighting to compute the temperature angular power spectrum. The WMAP mission has resulted in a highly constrained Delta CDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that big bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (N-eff = 3.84 +/- 0.40). The model fit also implies that the age of the universe is t(0) = 13.772 +/- 0.059 Gyr, and the fit Hubble constant is H-0 = 69.32 +/- 0.80 km s(-1) Mpc(-1). Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity, reported earlier by the WMAP team, now has high statistical significance (n(s) = 0.9608 +/- 0.0080); and the universe is close to flat/Euclidean (Omega(k) = -0.0027(-0.0038)(+0.0039)). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter Delta CDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness of fit, the inflationary flat Delta CDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology.Item Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: are there Cosmic Microwave Background Anomalies?(2011-02) Bennett, C. L.; Hill, R. S.; Hinshaw, G.; Larson, D.; Smith, K. M.; Dunkley, J.; Gold, B.; Halpern, M.; Jarosik, N.; Kogut, A.; Komatsu, Eiichiro; Limon, M.; Meyer, S. S.; Nolta, M. R.; Odegard, N.; Page, L.; Spergel, D. N.; Tucker, G. S.; Weiland, J. L.; Wollack, E.; Wright, E. L.; Komatsu, EiichiroA simple six-parameter Lambda CDM model provides a successful fit to WMAP data. This holds both when the WMAP data are analyzed alone or in combination with other cosmological data. Even so, it is appropriate to examine the data carefully to search for hints of deviations from the now standard model of cosmology, which includes inflation, dark energy, dark matter, baryons, and neutrinos. The cosmological community has subjected the WMAP data to extensive and varied analyses. While there is widespread agreement as to the overall success of the six-parameter Lambda CDM model, various "anomalies" have been reported relative to that model. In this paper we examine potential anomalies and present analyses and assessments of their significance. In most cases we find that claimed anomalies depend on posterior selection of some aspect or subset of the data. Compared with sky simulations based on the best-fit model, one can select for low probability features of the WMAP data. Low probability features are expected, but it is not usually straightforward to determine whether any particular low probability feature is the result of the a posteriori selection or non-standard cosmology. Hypothesis testing could, of course, always reveal an alternative model that is statistically favored, but there is currently no model that is more compelling. We find that two cold spots in the map are statistically consistent with random cosmic microwave background (CMB) fluctuations. We also find that the amplitude of the quadrupole is well within the expected 95% confidence range and therefore is not anomalously low. We find no significant anomaly with a lack of large angular scale CMB power for the best-fit Lambda CDM model. We examine in detail the properties of the power spectrum data with respect to the Lambda CDM model and find no significant anomalies. The quadrupole and octupole components of the CMB sky are remarkably aligned, but we find that this is not due to any single map feature; it results from the statistical combination of the full-sky anisotropy fluctuations. It may be due, in part, to chance alignments between the primary and secondary anisotropy, but this only shifts the coincidence from within the last scattering surface to between it and the local matter density distribution. While this alignment appears to be remarkable, there was no model that predicted it, nor has there been a model that provides a compelling retrodiction. We examine claims of a hemispherical or dipole power asymmetry across the sky and find that the evidence for these claims is not statistically significant. We confirm the claim of a strong quadrupolar power asymmetry effect, but there is considerable evidence that the effect is not cosmological. The likely explanation is an insufficient handling of beam asymmetries. We conclude that there is no compelling evidence for deviations from the Lambda CDM model, which is generally an acceptable statistical fit to WMAP and other cosmological data.Item Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Power Spectra and WMAP-Derived Parameters(2011-02) Larson, D.; Dunkley, J.; Hinshaw, G.; Komatsu, Eiichiro; Nolta, M. R.; Bennett, C. L.; Gold, B.; Halpern, M.; Hill, R. S.; Jarosik, N.; Kogut, A.; Limon, M.; Meyer, S. S.; Odegard, N.; Page, L.; Smith, K. M.; Spergel, D. N.; Tucker, G. S.; Weiland, J. L.; Wollack, E.; Wright, E. L.; Komatsu, EiichiroThe WMAP mission has produced sky maps from seven years of observations at L2. We present the angular power spectra derived from the seven-year maps and discuss the cosmological conclusions that can be inferred from WMAP data alone. With the seven-year data, the temperature (TT) spectrum measurement has a signal-to-noise ratio per multipole that exceeds unity for l < 919; and in band powers of width Delta l = 10, the signal-to-noise ratio exceeds unity up to l = 1060. The third acoustic peak in the TT spectrum is now well measured by WMAP. In the context of a flat Lambda CDM model, this improvement allows us to place tighter constraints on the matter density from WMAP data alone, Omega(m)h(2) = 0.1334(-0.0055)(+0.0056), and on the epoch of matter-radiation equality, z(eq) = 3196(-133)(+134). The temperature-polarization (TE) spectrum is detected in the seven-year data with a significance of 20 sigma, compared to 13 sigma with the five-year data. We now detect the second dip in the TE spectrum near l similar to 450 with high confidence. The TB and EB spectra remain consistent with zero, thus demonstrating low systematic errors and foreground residuals in the data. The low-l EE spectrum, a measure of the optical depth due to reionization, is detected at 5.5 sigma significance when averaged over l = 2-7: l(l+ 1)C-l(EE)/(2 pi) = 0.074(-0.025)(+0.034) mu K-2 (68% CL). We now detect the high-l, 24 <= l <= 800, EE spectrum at over 8 sigma. The BB spectrum, an important probe of gravitational waves from inflation, remains consistent with zero; when averaged over l = 2-7, l(l + 1)C-l(BB)/(2 pi) < 0.055 mu K-2 (95% CL). The upper limit on tensor modes from polarization data alone is a factor of two lower with the seven-year data than it was using the five-year data. The data remain consistent with the simple Lambda CDM model: the best-fit TT spectrum has an effective chi(2) of 1227 for 1170 degrees of freedom, with a probability to exceed of 9.6%. The allowable volume in the six-dimensional space of Lambda CDM parameters has been reduced by a factor of 1.5 relative to the five-year volume, while the Lambda CDM model that allows for tensor modes and a running scalar spectral index has a factor of three lower volume when fit to the seven-year data. We test the parameter recovery process for bias and find that the scalar spectral index, n(s), is biased high, but only by 0.09 sigma, while the remaining parameters are biased by <0.15 sigma. The improvement in the third peak measurement leads to tighter lower limits from WMAP on the number of relativistic degrees of freedom (e.g., neutrinos) in the early universe: N-eff > 2.7 (95% CL). Also, using WMAP data alone, the primordial helium mass fraction is found to be Y-He = 0.28(-0.15)(+0.14), and with data from higher-resolution cosmic microwave background experiments included, we now establish the existence of pre-stellar helium at >3 sigma. These new WMAP measurements provide important tests of big bang cosmology.